Transmission of working vehicle

ABSTRACT

An oil supply system for a transmission includes a transmission casing; a transmission shaft disposed in the transmission casing; a plurality of gears relatively rotatably fitted on the transmission shaft; an oil passage axially formed in the transmission shaft; a trough portion formed on an inside wall of the transmission casing so as to receive oil splashed from the gears; and a connection passage formed in a side wall of the transmission casing and extending downwardly from the trough portion to the oil passage. The oil passage is opened at outer peripheral portions of the transmission shaft adjacent to the gears, and opened at one axial end of the transmission shaft. The trough portion is disposed above the transmission shaft and is extended axially along the transmission shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/603,750, filed Jun. 26, 2003 now abandoned, which is a continuationof application Ser. No. 09/942,556, filed Aug. 31, 2001, now U.S. Pat.No. 6,616,563, issued Sep. 9, 2003, the entire disclosures of which areherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a transmissioncomprising a belt-type continuously variable transmission (hereafterreferred to as ‘CVT’), which is suitable for a working vehicle.

2. Background Art

A conventional working vehicle, e.g., a truck, includes a belt-type CVTconnecting an output shaft of an engine and an input shaft of thetransmission such that rotation of the output shaft of the engine istransmitted to its axles and drives them. In this vehicle structure, asensing mechanism is provided at the CVT and detects rotary speed orload of the engine so as to automatically steplessly reduce/increase thespeed reduction ratio according to the increase/decrease of rotary speedof the engine or the decrease/increase of the engine load.

In addition, it is well-known to laterally mount an engine on a vehicleso as to locate its crankshaft perpendicular to the longitudinaldirection of the vehicle and in parallel to an input shaft of atransmission, an output shaft of the transmission, and axles. Thisdescribed vehicle structure especially facilitates interposing abelt-type CVT between the crankshaft of the engine and the input shaftof the transmission because both shafts are parallel to each other.Moreover, the transmission in this vehicle structure may transmit powervia economical spur wheels because shafts therein are disposed parallelto one another. Therefore, the vehicle structure is advantageous incontributing to the reduction of assembly and material costs.

An object of the invention is to provide a transmission for a workingvehicle that is simplified so that the manufacturing costs can be moreand more reduced.

Further, conventional transmissions with differential locking mechanismsprovide a shaft for operating the differential locking mechanism that isaxially, slidably supported and is disposed parallel to the axles. Thedifferential locking slider is engaged with a fork fixed onto the shaftso as to slide the differential locking slider integrally with theshaft, thereby switching between a differential-locking mode and adifferential-unlocking mode.

However, in the above conventional structure, the fork engaged with thedifferential locking slider is apt to be large, thereby inhibitingminiaturization of the transmission. And, because a space inside of thetransmission housing is required for straightly moving such a large forkback and forth at a set stroke to operate the differential lockingslider, further miniaturization of the transmission is difficult.

BRIEF SUMMARY OF THE INVENTION

The transmission of the present invention is applied to a workingvehicle having an engine mounted on a bodywork frame such that acrankshaft of the engine is disposed horizontal to the ground and isperpendicular to the longitudinal direction of the vehicle. Thetransmission comprises an input shaft for receiving power of the enginethrough a CVT, an output shaft disposed in parallel with the inputshaft, a pair of left and right axles aligned with and extending outopposite to each other and in parallel with the output shaft, adifferential connecting the left and right axles with each other in adifferential manner, a transmission housing containing the differential,a pair of left and right axle housings mounted onto left and right facesof the transmission housing respectively, each of which houses each ofthe pair of axles, having mounting portions for mounting to the bodyworkframe, and a wet-type disc brake device provided around a portion of theaxles covered by the axle housings. Therefore, a load, which is appliedto drive wheels fixed on the axles, can be supported by the transmissionhousing through the axle housings, thereby simplifying the structure ofa vehicle. And, in comparison with the conventional structure having anoutput of a differential that is transmitted to the drive wheels throughuniversal joints and a dry-type brake device, manufacturing costs can bereduced. Furthermore, due to the wet type disc brake device, durabilityand reliability of the brake device can be improved.

The input shaft is disposed closer to the engine than said axles in thelongitudinal direction of the vehicle. Therefore, the position of theinput shaft, while keeping a required distance from the axles, can belower than that when being above the axles. Due to this arrangement,even if the amount of lubricating oil in the transmission housing issmall, splash lubrication for the input shaft can be sufficient.Consequently, the amount of lubricating oil can be saved, therebyreducing manufacturing costs and weight of the transmission. And, whenthe present invention is applied to a transmission of a truck, its deckcan be located at a low position, thereby improving capacity of the deckand sinking the center of gravity of the truck.

The transmission further comprises a drive train which can switch therotational direction of the output shaft in relation to the rotationaldirection of the input shaft, wherein the drive train drivingly connectsthe input shaft with a portion of the output shaft, which is nearer toone end of the output shaft, a prime rotary object provided on theoutput shaft nearer to other end of the output shaft, a follower rotaryobject serving as an input means of said differential, the followerrotary object being engaged with the prime rotary object, and acentrifugal governor for changing the output of the engine according tothe variation of the rotational speed of the input shaft, thecentrifugal governor being disposed at a portion of the input shaftfacing toward the prime rotary object. Therefore, by the adoption of thecentrifugal governor which is smaller and less expensive than a torquegovernor, manufacturing costs of the transmission can be saved andcompactness thereof can be improved. And, because the centrifugalgovernor is placed at empty space inside of the transmission housing, alayout of the transmission can be simple and space-saving, therebyfurther improving compactness of the transmission.

The transmission further comprises a pair of left and right transmissionhousing parts into which the transmission housing is laterally dividablethrough a surface which is perpendicular to a longitudinal direction ofsaid axles, wherein the differential is supported at its left and rightportions by the left and right transmission housing parts, respectively,and bearings provided at outer ends of the respective axle housings,wherein the bearings support outward portions of the axles projectingleftward and rightward from the differential. Therefore, because thedifferential can be directly supported by the transmission housingwithout intervention of the axles, when manufacturing of thetransmission, a convenient assembling method (i.e., a method of puttingin axles after fixing the differential to the transmission housing byjoining together of left and right housing parts) can be adopted.Furthermore, since outward portions of the axles are supported by theaxle housings through the bearings, the weight of the vehicle can besurely supported by the axles through the axle housings.

A portion of at least one of said the housings to be attached to thetransmission housing is expanded so as to be bowl-like shaped. Thewet-type disc brake is disposed in the bowl-like shaped portion of theaxle housing, and an arm for operating the wet-type disc brake isdisposed outside the bowl-like shaped portion of the axle housing.Therefore, because a room which houses the wet-type disc brake (i.e. thebowl-like shaped portion) is integrally formed with the axle housing,manufacturing costs of the transmission can be reduced. And, because thearm for operating the wet-type disc brake is disposed outside the bowlportion of the axle housing, the operating system from the arm towet-type disc brake can be compactly and simply formed.

A transmission of a working vehicle comprises a differential, atransmission housing containing the differential, a pair of left andright axles connected with each other in a differential manner by thedifferential, an axle housing mounted onto one of left and right facesof the transmission housings to support one of the axles, wherein ajoint space is formed in a joint portion between the transmissionhousing and the axle housing, a differential locking slider which canswitch between a differential mode for connecting the left and rightaxles with each other in a differential manner and adifferential-locking mode for integrally connecting the axles, afriction disc provided on the axle supported by the axle housing, and apressure member which pushes the friction disc so as to brake the axle,wherein the pressure member and the differential locking slider aredisposed substantially coaxially with each other in the joint space.Therefore, the differential locking slider and the pressure member canbe arranged in a compact length of longitudinal direction of the axles,thereby contributing to space-saving of the transmission.

A guide portion for axially slidably supporting said pressure member isprovided in a flanged portion formed on an outer side wall of thetransmission housing for mounting the axle housing, the differentiallocking slider is disposed in the guide portion, and a round wall of theguide portion is partly notched such that an arm for operating thedifferential locking slider is inserted through the notched portion.Therefore, because the pressure member is supported by the guide portionand the differential locking slider is located inside of the guideportion, both of them can be apportioned between inside and outside ofthe guide portion in a compact mass. And, because the round wall of theguide portion is partly notched and the arm for operating thedifferential locking slider is inserted through the notched portion, thesimple structure for operating the differential locking slider locatedin the guide portion from the outside of the guide portion can beachieved.

The pressure member is rotatable along said round wall of said guideportion by a brake operating shaft supported by said axle housing, and acam body, which thrusts the pressure member in correspondence to asrotational degree of the pressure member, is supported around the roundwall of the guide portion. Therefore, since the pressure member rotateswhile it is guided by an outer peripheral surface of the round wall ofthe guide portion, a special structure for axial alignment of thepressure member can be eliminated. And, since the cam body is supportedaround the round wall of the guide portion, the compact structure thatthe pressure member pushes the friction discs by axially sliding whilerotating can be achieved.

A rotational axis of the arm for operating the differential lockingslider is disposed at a position which is offset from a virtual planecontaining the rotational axis of said pressure member, and the brakeoperating shaft is placed in parallel with the axles on a opposite sideto the arm with the virtual plane between. Therefore, an operatingsystem of the differential locking slider and an operating system of thebrake device can be compactly arranged and can avoid interruptions witheach other, thereby miniaturizing the transmission.

Furthermore, the transmission further comprises an input shaftprojecting outward from one of left and right sides of said transmissionhousing and a follower pulley constituting a belt-type CVT disposed ontoan outward projecting portion of the input shaft, wherein saiddifferential locking slider is disposed at a position nearer to theother of the left and right sides of the transmission housing.Therefore, an operating system of the differential locking slider can bedisposed in a position wherein the operating system can avoidinterruptions with the CVT, thereby improving the compactness of thetransmission.

An oil supply system for the transmission comprises a transmissioncasing, an output shaft disposed in the transmission casing, a pluralityof gears relatively rotatably fitted on the output shaft, an oil passageaxially formed in the output shaft, a trough portion formed on an insidewall of the transmission casing so as to receive oil splashed from thegears, and a connection passage formed in a side wall of thetransmission casing and extending downwardly from the trough portion tothe oil passage. The oil passage is opened at outer peripheral portionsof the output shaft adjacent to the gears, and opened at one axial endof the output shaft. The trough portion is disposed above the outputshaft and extended axially along the output shaft. In one embodiment,the plurality of gears includes a normal gear and a reverse gear, and anautomatic continuously variable belt transmission is disposed outsidethe transmission casing. The normal gear and the reverse gear aredrivingly interposed between the belt transmission and the output shaftso that either the normal gear or the reverse gear is selectively fixedto the output shaft so as to determine one of opposite rotary directionsof the output shaft.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a general side view of a truck to which a transmission of thepresent invention is applied.

FIG. 2 is a sectional rear elevation showing the general structure ofthe transmission and axles.

FIG. 3 is a grossly enlarged sectional rear elevation showing thestructure in a transmission housing.

FIG. 4 is a side view of the transmission.

FIG. 5 is a sectional side view of the transmission.

FIG. 6 is a sectional side view of the transmission when modified axlehousings are attached.

FIG. 7 is a general side view of a truck having a transmission wherein adifferential locking mechanism is provided.

FIG. 8 is a sectional rear development showing the structure in atransmission housing.

FIG. 9 is a perspective view showing the state wherein axle housings aredetached from a transmission housing.

FIG. 10 is a sectional rear view showing a transmission of the typewhich receives power from an electric motor.

FIG. 11 is a segmentary perspective view showing the structure forholding friction discs to an axle housing in the brake device of thetransmission of electric motor type.

FIG. 12 is a grossly enlarged sectional rear development mainly showingthe structure of a clutch fork shaft and an idle gear.

FIG. 13 is a sectional side view showing the structure that adifferential shift arm is inserted through a partly notched portion ofthe guide portion.

FIG. 14 is a sectional side view mainly showing the structure of adirection-switching shaft.

FIG. 15 is a perspective view showing a right housing member composingthe transmission housing.

FIG. 16 is a perspective view showing a pressure member.

FIG. 17 is a sectional plan development showing brake control shafts.

FIG. 18 is a sectional rear view showing the structure for leadinglubricating oil to an output shaft.

DETAILED DESCRIPTION OF THE INVENTION

A truck 1 as an embodiment of the present invention is shown in FIG. 1.A bodywork frame 10 is disposed in the longitudinal direction of thevehicle. An engine 3 is mounted on the bodywork frame 10 at the rear ofan operator's seat 2. The engine 3 is disposed such that its crankshaft(as an output shaft of the engine) 6 is horizontally orientedperpendicular to the longitudinal direction of the vehicle.

At the rear of the engine 3, a transmission 4 of the present inventionis supported by the bodywork frame 10 through a pair of axle housings 80(described below). A pair of left and right slender flat boards aredisposed in a longitudinal direction of the vehicle and parallel to eachother, and the rear end portion of the flat boards are connected witheach other, thereby forming the bodywork frame 10 having a U-shape in aplan view. As shown in FIG. 2, axle housings 80 are fixed onto thebodywork frame 10 such that a housing 31 of the transmission 4 islocated between the left and right flat boards.

A deck frame 10 a is disposed above the transmission 4 and the engine 3,and is supported by the bodywork frame 10, such that the truck can carryloads.

An input shaft 5 of the transmission 4 projects leftward from thetransmission housing 31. The input shaft 5 is connected to the outputshaft 6 of the engine 3 through a belt-type automatically continuousvariable transmission (hereinafter referred to as CVT) 7. A pair of leftand right rear axles 8 project outward from both left and right sides ofthe transmission housing 31. Each of rear wheels 9 as drive wheels isprovided at the outer end of each of the rear axles 8.

A front transaxle case (not shown) is supported at a front portion ofthe vehicle. The front transaxle case houses a pair of left and rightfront axles 11, and a differential (not shown) which connects the frontaxles 11 with each other in a differential manner. Each of the frontaxles 11 supports each of front wheels 12 at its outer end. The frontwheels 12 are steerable by a steering wheel 13 disposed at the front ofthe operator's seat 2.

A switching lever 19, which is operated to select the direction oftravel between forward and backward, is disposed at the side of thesteering wheel 13. A speed-changing pedal 21 is provided at the front ofthe operator's seat 2, and is linked with a throttle valve (not shown)which adjusts the volume of injected fuel. By changing the degree ofopening of the throttle valve according to degree of depressing of thespeed-changing pedal 21, the output speed of the engine 3 can beincreased or reduced.

The power, which is transmitted from the output shaft 6 to the inputshaft 5 of the transmission 4 through the CVT 7, is transmitted into thetransmission housing 31 through the input shaft 5. The power passesthrough a power transmission way which forming the transmission 4, andis finally transmitted to the rear wheels 9 through the rear axles 8,thereby driving the truck 1.

A pair of brake devices (not shown in FIG. 1) are provided in the axlehousings 80 so as to brake the pair of left and right rear axles 8,respectively. Each of the brake devices 22 can be operated by each of apair of brake control arms 23 which are supported rotatably on each ofthe left and right axle housings 80. The brake control arms 23 areinterlocked with only one brake pedal (not shown) disposed in thevicinity of the speed-changing pedal 21, such that the left and rightrear axles 8 are braked at the same time by depressing the brake pedal.

Next, description will be given on the structure in the transmissionhousing 31 in accordance with FIG. 2.

The transmission housing 31, which houses the transmission 4, is formedof a pair of left and right housing members 31L and 31R (serving astransmission housing parts) which are joined to each other at their flatand peripheral joint faces in a plane which is perpendicular to alongitudinal direction of the rear axles 8. In the transmission housing31, the input shaft 5, a centrifugal governor 34 which detects therotational speed of the input shaft 5, a differential 32 which connectsthe left and right rear axles 8 in a differential manner, and adirection-of-travel switching mechanism 35 operated by the switchinglever 19, and so on are disposed.

The input shaft 5 is laterally and rotatably supported at the midwayportion in a vertical direction of the transmission housing 31. One endof the input shaft 5 projects laterally outward from a left side of thetransmission housing 31. A follower split pulley 36 is provided on theoutward projecting portion of the input shaft 5, such that the followersplit pulley 36 serves as an output section of above-mentioned belt-typeCVT 7.

The follower split pulley 36 is formed of two pulley members 36 a and 36b which are connected with each other forming torque cam as shown inFIG. 3. The two pulley members 36 a and 36 b approach each other whentorque which resists the rotation of the engine 3 (e.g. torque generatedat the rear wheels 9 when the truck 1 climbs a hill) increases, suchthat an effective diameter of the follower split pulley 36 increases soas to increase the speed reduction ratio of the CVT 7.

Next, description will be given on the centrifugal governor 34.

This centrifugal governor 34, disposed around a portion of the inputshaft 5 facing toward a later-discussed output gear 51, comprises agovernor weight 71, a lifter 72, a governor fork 73, a rotation shaft 74and an output arm 75. The governor weight is a sensor which is rotatedoutward according to centrifugal force so as to detect the rotationalspeed of the input shaft 5. The lifter 72 is slidden axially at the sametime when the governor weight 71 rotates outward. The governor fork 73is engaged with the lifter 72. The rotation shaft 74 is supportedrotatably at the ceiling of the transmission housing 31. The output arm75 is disposed on the outside of the transmission housing 31 so as torotate integrally with the rotation shaft 74.

The output arm 75 is interlocked with the throttle valve of the engine 3through a linkage, such that the centrifugal governor 34 detects therotational speed of the input shaft 5 and adjusts the volume of injectedfuel, thereby changing the output of the engine 3 according to thevariation of the rotational speed of the input shaft 5.

Next, description will be given on the direction-of-travel switchingmechanism 35 serving as a drive train to allow switching the rotationaldirection of the output shaft 37 in relation to the rotational directionof the input shaft 5.

The input shaft 5 is notched on its periphery so as to form two gears,i.e., a forward drive gear 39 and a reverse drive gear 40. The outputshaft 37 is disposed parallel to the input shaft 5 (and the rear axles8). Around a portion of the output shaft 37 which is nearer to the leftend of the output shaft 37, a forward follower gear 43 is relativelyrotatably disposed, and a clutch gear 44 are not relatively rotatablybut axially slidably disposed. The forward follower gear 43, which isconstantly engaged with the forward drive gear 39, is notched on itsside face so as to form a toothed portion 43 a, thereby beingengaged/disengaged with/from a toothed portion 44 a formed on the sideface of the clutch gear 44 facing the toothed portion 43 a.

An idle gear 45, designated by a phantom line in FIG. 3, is constantlyengaged with the reverse drive gear 40. The clutch gear 44 also can beengaged/disengaged with/from the idle gear 45.

The clutch gear 44 is axially slid so as to engage with either theforward follower gear 43 or the idle gear 45, thereby selectivelybringing the output shaft 37 into a regularly directed rotation or areversely directed rotation.

As shown in FIG. 5, a clutch fork shaft 48 is straightly, slidablydisposed adjacent to the clutch gear 44, and a clutch fork 49 is fixedonto the clutch fork shaft 48 and is engaged with the clutch gear 44. Acontrol shaft 60 is vertically and rotatably supported at the ceiling ofthe transmission housing 31 so as to slide the clutch fork shaft 48. Anarm 61 is fixed onto a bottom portion of the control shaft 60 and anapex portion of the arm 61 is engaged with a groove formed on the clutchfork shaft 48. A top portion of the control shaft 60 projects upward,and an operating arm 62 is fixed onto the upward projecting portion ofthe control shaft 60. The operating arm 62 is interlocked with theabove-mentioned switching lever 19, thereby allowing the clutch gear 44to slide to a forward position or a backward position.

A portion of the output shaft 37, which is nearer to the right end ofthe output shaft 37, is notched on its periphery so as to form theoutput gear 51 serving as a prime rotary object, thereby transmittingthe rotation of the output shaft 37 to the differential 32.

The differential 32 is constructed normally for differentiallyconnecting inner end portions of the pair of rear axles 8, which extendoppositely to each other. In detail, as shown in FIG. 3, thedifferential 32 comprises a hollow differential casing 52, a ring gear53, a pinion shaft 54, two pinions 55, and two differential side gears56. The differential casing 52 is disposed coaxially with the rear axles8, and rotatably supported at its left and right portions by the leftand right housing members 31L and 31R through bearings 111,respectively. The ring gear 53, serving as a follower rotary object, isfixed around the differential casing 52 and is engaged with the outputgear 51 of the output shaft 37. The pinion shaft 54 is disposed in thedifferential casing 52 perpendicular to the rear axles 8 so as to berotatable integrally with the differential casing 52. The pinions 55,which are bevel gears, are disposed oppositely to each other androtatably supported on the pinion shaft 54. Each of the differentialside gears 56 which are bevel gears is fixed onto an inner end of eachof the rear axles 8 so as to engage with both the pinions 55.

Next, the axle housings 80, each of which supports each of the rearaxles 8, will be described.

The two axle housings 80 are formed in the same cylindrical shape. Asshown in FIG. 2, an inner end of each of the axle housings 80 issymmetrically fixed onto each of left and right sides of thetransmission housing 31, so as to cover an opening portion formed oneach of the left and right side faces of the transmission housing 31. Anouter end of each of the axle housings 80 projects outward along therear axles 8. A supporting portion is formed at the projecting endportion of each of the axle housings 80 so as to support an outwardportion of each of the rear axles 8 by a bearing 110. Thus, a portion ofeach rear axle 8 adjacent to its proximal end is covered at a certainlength with each axle housing 80.

A top portion of the supporting portion of each of the axle housings 80is formed into a mounting portion 80 a having a horizontally flat shape.The mounting stay 81 in a flat-board-like shape, which is fixed onto abottom end of the bodywork frame 10, is fixed onto the mounting portion80 a by screwing bolts so as to support the axle housings 80 by thebodywork frame 10. In such a structure, a load applied to the rearwheels 9 can be supported by the transmission housing 31 through theaxle housings 80, thereby simplifying the structure of a vehicle.

As shown in FIG. 3, left and right brake devices 22, for braking therear axles 8, is provided around portions of the rear axles 8 covered bythe axle housings 80, respectively. Portions of the axle housings 80 tobe attached to the transmission housing 31 are expanded so as to bebowl-like shaped. Each of brake devices 22 is housed in each ofbowl-like shaped portions 80 b.

In each of the brake devices 22, first friction disc 91 are axiallyslidably but not relatively rotatably provided onto the rear axle 8.And, second friction discs 92 are slidably but not relatively rotatablyengaged with the axle housing 80. Each of the first friction discs 91and each of the second friction discs 92 are arranged alternately. Apressure member 93 is fitted axially slidably and rotatably onto thetransmission housing 31 for pressuring the multi-layered friction discs91 and 92. Cam grooves are formed on the pressure member 93, and each ofsteel balls 94, serving as cam bodies, is intervened between each of thecam grooves and the axle housing 80. A brake control shaft 96 isrotatably supported by the axle housing 80, and a cam is formed at oneend portion of a brake control shaft 96 in a D-shape (not shown) so asto push an arm 95 formed at a top portion of the pressure member 93. Theabove-mentioned brake control arm 23 is fixed onto one end of the brakecontrol shaft 96, which projects outward from the axle housing 80. Thebrake control arm 23 is disposed outside above-mentioned bowl-likeshaped portion 80 b.

In this structure, when the brake control arm 23 is operated, the brakecontrol shaft 96 is rotated and the above-mentioned D-shape cam pushesthe arm 95 so as to rotate the pressure member 93. By the action of cambetween the cam groove and the steel ball 94, the pressure member 93 isslidden axially and make the friction discs 91 and 92 engage with oneanother, thereby braking the rear axle 8.

The axle housings 80 and the transmission housing 31 are filled withoil, i.e., the brake devices 22 are of a wet type, thereby beingimproved in its durability and reliability.

The input shaft 5 is displaced from a position above the rear axles 8 soas to be nearer to the engine 3 than the rear axles 8 in thelongitudinal direction of the vehicle such that the position of theinput shaft 5 can be lowered in the transmission housing 31.Consequently, even if the amount of the filled oil is small and oillevel OL is low, splash lubrication for the input shaft 5 by therotation of the ring gear 53 of the differential 32 can be sufficientbecause the input shaft 5 is located at the low position.

Various modification of the above-mentioned embodiment is possible. Forexample, as shown in FIG. 6, the structure that axle housings 80′ arefixed onto the transmission housing 31 leaning forward or backward so asto locate the brake control arm 23 at a low position, may be available.

Next, description will be given on a transmission 4′ wherein adifferential locking mechanism is provided. A truck to which thetransmission 4′ is applied is shown in FIG. 7.

As shown in FIGS. 8 and 9, each of the left and right housing members31L and 31R is formed at its outer side wall into each of left and rightcylindrically flanged portions 31La and 31Ra which are extendedlaterally outward. The outer end surface of each of the cylindricallyflanged portions 31La and 31Ra is formed into a vertical flat jointface, on which the above-mentioned axle housing 80 is mounted.

As shown in FIG. 8, a hole 97 is formed on the side wall of the righthousing member 31R, and one end portion of an input shaft 5′ of thetransmission 4′ is supported in the hole 97 through a bearing. As shownin FIG. 10, a mounting surface 98, onto which an electric motor 99 ismounted through a bracket 100, is formed on an outer face of the sidewall around of the hole 97 of the right housing member 31R. Namely, thehousing members 31L and 31R are available for both of an engine type andan electric motor type. Reference numerals 101 in FIGS. 8 and 9designate as mounting bosses formed on the right housing member 31R forscrewing the bracket 100 onto the mounting surface 98.

In the engine type shown in FIG. 8, which receives power from the engine3 through the CVT 7, the input shaft 5′ projects outward through theside wall of the left housing member 31L, and the hole 97 in the righthousing member 31R is closed by a cover 102.

On the other hand, in the electric motor type shown in FIG. 10, an inputshaft 5″ projects outward through the hole 97 and is connected with amotor shaft 103 of the electric motor 99 through a coupler 104. In thistype, a cover 106 closes a hole 105 in the left housing member 31L.

In the electric motor type, the direction-of-travel switching mechanism35 (as provided in the engine type) is removed, and the input shaft 5″and an output shaft 37′ are constantly engaged with each other through agear 44′. Because, the electric motor 99 itself can bring the inputshaft 5″ into a regularly directed rotation or a reversely directedrotation selectively.

The engine type will be described in accordance with FIG. 12 andgreater. As shown in FIG. 12, the idle gear 45 in thedirection-of-travel switching mechanism 35 is supported rotatably on ashaft 14. A left end of the shaft 14 is supported by a boss formed onthe inner face of the side wall of the left housing member 31L. As shownin FIGS. 12, 14, and 15, the joint surface, which is formed on the lefthousing member 31L to join with the right housing member 31R, partlyprojects inward of the transmission housing 31. A support plate 30 isscrewed to the projected portion, and a right end of the shaft 14 isinserted and fitted into a circular hole 30 a formed in the supportplate 30.

In this structure, the shaft 14 is rattle-free because the both ends ofthe shaft 14 are supported. And, the shaft 14 is not required to be solong as a whole width of the transmission housing 31, thereby improvingcompactness. Other mechanics (in this embodiment, the rotation shaft 74and the governor fork 73 of the centrifugal governor 34) can be placedin such formed empty space.

As shown in FIGS. 8 and 12, a forward follower gear 43 and a backwardfollower gear 44 are relatively rotatably supported around the outputshaft 37′. The forward follower gear 43 is constantly engaged with theforward drive gear 39 formed around the input shaft 5′, and backwardfollower gear 44 is with the reverse drive gear 40 through the idle gear45.

Between the two follower gears 43 and 44, a clutch slider 47 is notrelatively rotatably but axially slidably disposed around the outputshaft 37′. The clutch slider 47 is axially slidden so as to engage witheither the forward follower gear 43 or backward follower gear 44,thereby selectively bringing the output shaft 37′ into a regularlydirected rotation or a reversely directed rotation. Also, the clutchslider 47 can be located at its neutral position where it engages withnone of the two gears 43 and 44.

The clutch fork shaft 48 is straightly slidably supported by thetransmission housing 31, as shown in FIG. 12. The clutch slider 47 isengaged with the clutch fork 49 which is fixed onto the midway portionof the clutch fork shaft 48.

As shown in FIGS. 9 and 14, a direction-switching shaft 50 is verticallysupported at the ceiling of the right housing member 31R. An arm 46 isfixed onto the end portion of the direction-switching shaft 50 in thetransmission housing 31. An apex end portion of the arm 46 is engagedwith the groove notched on a midway portion of the clutch fork shaft 48.The speed-changing lever (not shown), which is interlocked with theswitching lever 19 provided beside the operator's seat 2 of vehicle, isfixed onto an external-of-housing end portion of the direction-switchingshaft 50.

In the above structure, the clutch slider 47 can be slidden among aforward-driving position, a backward-driving position and a neutralposition according to operation of the switching lever 19.

A detent mechanism 66 is provided with the clutch fork shaft 48 to keepits operating positions. The detent mechanism 66 comprises three grooves48 a notched on the clutch fork shaft 48 in correspondence to theabove-mentioned three operating positions (the forward-driving position,the backward-driving position and the neutral position), and a detentball 67 biased by spring so as to engage with one of the three grooves48 a.

An electrical switch 68 is provided with the clutch fork shaft 48 so asto detect its neutral position. The switch 68 is electrically connectedwith a circuit for starting a cell motor of the engine 3, therebyallowing the engine 3 to start only when the clutch fork shaft 48 islocated in its neutral position.

Next, description will be given on a differential 32′. The differential32′ is constructed almost similarly with the differential 32 ofabove-mentioned embodiment, except that a differential locking mechanism33 is provided.

The differential locking mechanism 33 is provided for locking thedifferential 32′. As shown in FIG. 8, a differential locking slider 57is axially slidably provided around the right rear axle 8 on theopposite side to the differential casing 52 with the ring gear 53between. A dog clutch portion 58 is formed on the surface of thedifferential locking slider 57 facing the ring gear 53. An engagingportion 59 is formed at a boss of the ring gear 53 so as to engage withthe dog clutch portion 58.

In this structure, the differential locking mechanism 33 can be selectedamong the differential-locked mode wherein the dog clutch portion 58 isengaged with the engaging portion 59 and the differential casing 52 isconnected integrally with the left and right rear axles 8, and thedifferential-unlocked mode wherein the dog clutch portion 58 isdisengaged from the engaging portion 59 and the differential 32′connects the rear axles 8 in a differential manner.

As shown in FIGS. 9 and 13, a differential control shaft 63 is rotatablyand vertically supported by the right housing member 31R. A differentialshift arm 64, the apex end of which is engaged with the differentiallocking slider 57, is fixed onto one end of the differential controlshaft 63 which projects in an inward direction of the transmissionhousing 31.

A differential locking control arm 65 is fixed onto one end of thedifferential control shaft 63 which projects in an outward direction ofthe transmission housing 31. The differential locking control arm 65 isconnected to the differential-locking operating tool (not shown)provided beside the operator's seat 2 through a linkage etc., therebyallowing operating to bring the differential 32′ into either a lockedmode or an unlocked mode.

Next, the brake devices 22′ in this embodiment will be described.

As shown in FIG. 8, the boss of the ring gear 53 is supported by theside wall of the right housing member 31R, and a boss of thedifferential casing 52 is by the side wall of the left housing member31L. Both of the side walls project cylindrically in an outwarddirection, thereby forming above-mentioned flanged portions 31La and31Ra. The cylindrically flanged portions 31La and 31Ra, formed formounting the axle housing 80, forms its internal space into empty space(hereafter referred to as ‘jointing space’).

Besides, in above-mentioned ‘jointing space’, left and right outer wallsof the housing members 31L and 31R project cylindrically in a laterallyoutward direction, thereby forming guide portions 31Lb and 31Rb. A pairof left and right pressure members 93 are fitted around the guideportions 31Lb and 31Rb respectively, and supported relatively rotatablyand axially slidably. Each of the pressure members 93 has a ring-shapeas shown in FIG. 16, and its internal diameter is equal to an externaldiameter of the guide portions 31Lb and 31Rb. Two hooks 93 a are formedon the external periphery of each of the pressure members 93.

The differential locking slider 57 is placed in the guide portions 31Rbof the right housing member 31R.

As shown in FIGS. 8, 9, 13, and 17, a pair of brake control shafts 96are rotatably supported above the pressure members 93 in parallel withthe rear axles 8. An inner end portion of each of brake control shafts96 is supported by a boss 17 formed on the side wall of each of left andright housing members 31L and 31R. An outer end portion of each of thebrake control shafts 96 is supported by each of the axle housings 80 andprojects outward. The above-mentioned brake control arm 23 is fixed ontothe outward projecting portion of the brake control shaft 96.

As shown in FIG. 13, a midway portion of the brake control shaft 96,which faces one of the two hooks 93 a of the pressure member 93, isformed into a cam having a D-shape. In this structure, when the brakecontrol arm 23 is operated and the brake control shaft 96 are rotated,the cam pushes the hook 93 a, thereby the pressure member 93 is rotatedaround the guide portion 31Lb (31Rb).

As shown in FIG. 8, a plurality of depressions, each of which is formedinto a hemispherical shape, are arranged at regular intervals incircumference on the side wall of the left housing member 31L at theoutside of the guide portion 31Lb. And, as shown in FIGS. 8 and 13, aplurality of ball retaining portions 70 project from the side wall ofthe right housing member 31R in correspondence to above-mentioneddepressions. A depression, having a hemispherical shape, is formed oneach of the ball retaining portions 70.

In correspondence to the position of the depressions, a plurality ofdepressions 93 b are formed and arranged at regular intervals incircumference on one side face as shown in FIG. 16. Each of thedepressions 93 b looks like a lozenge in a side view and like a cone ina sectional view, such that the depth of the depression 93 b is thegreatest at a center portion in circumference.

A steel ball 94 is supported by each of the hemispherical depressions ofthe housing member 31L (31R), and the pressure member 93 is fittedaround the guide portion 31Lb (31Rb) such that each of the steel balls94 is fitted into each of the depressions 93 b. The each ofabove-mentioned friction discs 91 and 92 are disposed between the otherside face of the pressure member 93 and the inner side face of the axlehousing 80.

In this structure, when the pressure member 93 is rotated along an outerperipheral surface of the guide portion 31Lb (31Rb) by the operation ofbrake control arm 23, the pressure member 93, onto which the cam actionof the steel balls 94 is applied, gets thrust (greater as its rotationaldegree increases) and is slidden outward, thereby pressuring thefriction discs 91 and 92 and braking the rear axles 8.

A projection 92 a is formed at a portion of each disc of the secondmulti friction discs 92. Each of these projections 92 a is engaged witha recess formed on inner surface of the axle housing 80. As shown inFIGS. 8 and 9, a holding hook 107 is fixed in the vicinity of therecess. An apex end of the holding hook 107 holds the projection 92 a ofan innermost disc of the second friction discs 92.

In above structure, when manufacturing of the transmission 4, each ofthe brake devices 22′ can be installed in the each of the axle housings80, and the holding hook 107 can prevent the friction discs 91 and 92from being detached from the axle housing 80, thereby forming anassemblage of axle housing 80 and brake device 22′ as shown in FIG. 9.Therefore, the transmission 4′ can be simply assembled by mounting leftand right such assemblages on the transmission housing 30.

Instead of the holding hook 107, the structure that an elastic wirehaving a U-like shape is fitted into two holes formed on the axlehousing 80 such that the wire strides the projection 92 a, is available.This structure is applied on the above-mentioned electric motor type asshown in FIGS. 10 and 11.

In this electric motor type, a distance between the two holes 109 formedon the axle housing 80 is a little shorter than a distance between bothends of the wire 108. Thus, when the wire 108 is fitted into two holes109, the wire transforms such that its both ends approach each other. Afriction force is generated between the fitted wire 108 and the twoholes 109 by an elasticity of the wire 108 such that the wire 108 doesnot detach from the axle housing 80 and can hold the friction discs 91and 92 of the brake device 22′.

The guide portion 31Rb is formed wider than the guide portion 31Lb, andthe external diameter of the differential locking slider 57 is smallerthan the internal diameter of the guide portion 31Rb (namely, smallerthan the internal diameter of the pressure member 93). The differentiallocking slider 57 is provided at the inner space of the guide portion31Rb, and is overlapped with the pressure member 93 in a longitudinaldirection of the rear axles 8.

In this structure, the pressure member 93 and the differential lockingslider 57 are provided in the above-mentioned ‘jointing space’. And,because each of the guide portions 31Lb and 31Rb is cylindrically formedcoaxially with a rotational axis of the rear axles 8, the rotationalaxis of the pressure member 93 is substantially coaxial with an axis ofthe differential locking slider 57 provided on the rear axle 8.

Thus, the differential locking slider 57 and the pressure member 93 canbe disposed in a compact mass, thereby enhancing the transmission 4′ inits compactness.

As shown in FIGS. 8 and 13, the differential locking slider 57 isdisposed at inner space of the guide portion 31Rb of the right housingmember 31R. As shown in FIGS. 9 and 13, the guide portion 31Rb is formedsuch that its cylindrical wall is partly notched, thereby forming anopening portion 15. The differential shift arm 64 is inserted throughthe opening portion 15, and an apex portion of the differential shiftarm 64 is engaged with the differential locking slider 57.

As shown in FIG. 13, the differential control shaft 63, onto which thedifferential shift arm 64 is fixed, is disposed at a position which isoffset from a virtual plane P containing the rotational axis of thepressure member 93. Therefore, the rotational axis of the differentialcontrol shaft 63 and the rotational axis of the differential shift arm64 are disposed in skewed direction with each other and do not cross.

Thus, the differential locking slider 57 can be slidden through therotation of the differential control shaft 63 and the differential shiftarm 64. The only small space needed for rotation of the differentialshift arm 64 is sufficient for operating the differential locking slider57 in the transmission housing 31.

On the other hand, in the structure that the differential locking slider57 is engaged with a shift fork which is slidden straightly, a largespace is needed for shifting the shift fork, thereby inhibitingminiaturization of the transmission. The structure of this embodimentsolves this issue.

In this embodiment, the brake control shaft 96 is placed on the oppositeside to the differential control shaft 63 with the virtual plane Pbetween. By this layout, a differential-locking operating system and abrake operating system can be disposed in a compact mass, and also canavoid interruptions with each other.

As shown in FIG. 8, the cylindrical flanged portion 31Ra and the guideportion 31Rb of the right housing member 31R are formed wider than theportions 31La and 31Lb of the left housing member 31L, because thedifferential locking slider 57 is disposed in the guide portion 31Rb. Asshown in FIGS. 9 and 13, the electrical switch 68, the differentialcontrol shaft 63, and a breather cap 16 for bleeding of air are disposedat the widely-formed cylindrical flanged portion 31Ra, thereby achievingthe rational layout for miniaturization of the transmission 4′.

In this embodiment, each of the axle housings 80 is formed symmetricallywith respect to the virtual vertical plane which includes the axis ofthe rear axles 8. Thus, two members of uniform shape can be used forboth of left and right axle housings 80, thereby reducing theirmanufacturing costs.

Furthermore, a pair of front and rear holes, formed on side walls of therespective axle housings 80, are arranged symmetrically with respect toabove-mentioned virtual vertical plane. And, in the structure that axlehousings 80 are disposed left and right, each of the front holessupports each of left and right brake control shafts 96, and each of therear holes is covered by a cap 86 as shown in FIG. 9. Thus, the left andright brake control shafts 96 can be coaxially disposed, and left andright brake systems can be rationally symmetrically arranged.

Furthermore, two hooks 93 a, formed on each of the pressure members 93,are arranged symmetrically as shown in FIG. 16. Thus, two members ofuniform shape can be used for both of left and right pressure members93, thereby reducing their manufacturing costs.

Next, the structure for lubrication of the transmission 4′ will bedescribed.

The transmission housing 31 is filled with lubricating oil inestablished amount, and an oil level OL is determined as shown in FIG.14. In this state, when the transmission 4′ is driven and the ring gear53 and a forward follower gear 43 rotate in the direction designating asa bold arrow in FIG. 14, the oil is splashed on the input shaft 5′ andthe output shaft 37, which are disposed at upward slant position of thering gear 53.

As shown in FIGS. 14 and 18, a trough portion 24, having a V-shape in aninterior side view, is formed on an inner face of side wall of the righthousing member 31R. An oil leading hole 76 is formed in a horizontaldirection on the portion of the right housing member 31R which faces abase of the trough portion 24. The oil leading hole 76 communicates witha connecting hole 77, which is formed vertically in the side wall of theright housing member 31R. The connecting hole 77 is connected with agroove 78, which is formed in a boss of the right housing member 31R forsupporting an end of the output shaft 37′.

In this structure, a part of the splashes of oil by rotation of the ringgear 53 etc. reaches above the trough portion 24, and flows along theoil leading hole 76 and the connecting hole 77 and is led to the groove78, thereby lubricating a bearing which supports the output shaft 37′.And, a part of the oil flows along an oil path (designated as areference numeral 87 in FIG. 12), and lubricates the peripheral surfaceof the output shaft 37′ for rotatably supporting the follower gears 43and 44, and a engaging portion of the clutch slider 47.

As shown in FIGS. 14 and 18, a lubricating inlet 82 is disposed justabove the trough portion 24. Therefore, when a cap 20 is taken off andlubricating oil is run in through the lubricating inlet 82, all thelubricating oil falls into the trough portion 24. A part amount of thelubricating oil can surely reach the groove 78 through the oil leadinghole 76 and the connecting hole 77 and can lubricate the bearingsupporting the output shaft 37′ and so on.

In this structure, even if components (e.g. the bearing for supportingthe output shaft 37, the follower gears 43 and 44, the clutch slider 47)are not spread with the lubricating oil in advance of assembling thetransmission 4′, these components are surely lubricated by only runningthe oil in through the lubricating inlet 82 after assembling thetransmission 4′. Therefore, the number of man-hours for manufacturingcan be reduced.

A hole 27 is formed at the bottom of side wall of the right housingmember 31R as shown in FIG. 13. An inner space of the transmissionhousing 31 and an inner space of the right axle housing 80 communicatewith each other through the hole 27 such that the oil with which boththe inner space are filled can circulate between.

Furthermore, two holes 25 and 26 are formed at the top of side wall ofthe right housing member 31R. An inner space of the transmission housing31 and an inner space of the right axle housing 80 also communicateswith each other through the two holes 25 and 26 such that the air inboth the inner space can circulate between. Thus, the air in the rightaxle housing 80 can be exhaled from the breather cap 16 disposed on thetransmission housing 31.

Similarly, holes are formed on the side wall of the left housing member31L (not shown). Therefore, the oil and air can circulate between theinner space of the transmission housing 31 and an inner space of theleft axle housing 80.

As shown in FIG. 13, the breather cap 16 is disposed at the ceilingportion of the right housing member 31R. An opening portion 83 forinstalling the breather cap 16 is separated off by an inner wall 84 fromthe inner space of the transmission housing 31, and a small hole 85 isformed on the inner wall 84.

In this structure, the air in the transmission housing 31 cancommunicate with the atmosphere through the small hole 85 and thebreather cap 16. And, even if the oil filled with the transmissionhousing 31 is stirred and splashed around, a splash of the oil isblocked by the inner wall 84 before reaching the breather cap 16,thereby preventing oil-leak from the breather cap 16.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form may be changed in the details ofconstruction, and the combination and arrangement of parts may bechanged or altered without departing from the spirit and the scope ofthe invention as hereinafter claimed.

1. An oil supply system for a transmission comprising: a transmissioncasing; an output shaft disposed in the transmission casing; a pluralityof gears relatively rotatably fitted on the output shaft; an oil passageaxially formed in the output shaft, wherein the oil passage is opened atouter peripheral portions of the output shaft adjacent to the gears, andopened at one axial end of the output shaft; a trough portion formed onan inside wall of the transmission casing so as to receive oil splashedfrom the gears, wherein the trough portion is disposed above the outputshaft and extended axially along the output shaft; a connection passageformed in a side wall of the transmission casing and extendingdownwardly from the trough portion to the oil passage; an automaticcontinuously variable belt transmission disposed outside thetransmission casing, and wherein the plurality of gears includes anormal gear and a reverse gear, wherein the normal gear and the reversegear are drivingly interposed between the belt transmission and theoutput shaft so that either the normal gear or the reverse gear isselectively fixed to the output shaft so as to determine one of oppositerotary directions of the output shaft.
 2. An oil supply system for atransmission comprising: a transmission casing; an output shaft disposedin the transmission casing; a plurality of gears relatively rotatablyfitted on the output shaft; an oil passage axially formed in the outputshaft, wherein the oil passage is opened at outer peripheral portions ofthe output shaft adjacent to the gears, and opened at one axial end ofthe output shaft; a trough portion formed on an inside wall of thetransmission casing so as to receive oil splashed from the gears,wherein the trough portion is disposed above the output shaft andextended axially along the output shaft; a connection passage formed ina side wall of the transmission casing and extending downwardly from thetrough portion to the oil passage; a pair of casing parts joined to eachother so as to constitute the transmission casing, wherein the troughportion is convex and is formed on one of the casing parts; and a pairof opposite axles, supported by the transmission casing and driven bythe output shaft, wherein the casing parts are joined to each other at ajoint surface disposed at the middle position between the axles, andwherein the trough portion is extended to the joint surface.
 3. An oilsupply system for a transmission comprising: a transmission casing; anoutput shaft disposed in the transmission casing; a plurality of gearsrelatively rotatably fitted on the output shaft; an oil passage axiallyformed in the output shaft, wherein the oil passage is opened at outerperipheral portions of the output shaft adjacent to the gears, andopened at one axial end of the output shaft; a trough portion formed onan inside wall of the transmission casing so as to receive oil splashedfrom the gears, wherein the trough portion is disposed above the outputshaft and extended axially along the output shaft; a connection passageformed in a side wall of the transmission casing and extendingdownwardly from the trough portion to the oil passage; a breatherdisposed at a top portion of the transmission casing; and at least twolayered partition walls disposed below the breather and extended axiallyalong the output shaft so as to allow air to or from the breathertherethrough.